It has been known for some time in the prior art to provide can ends which can be opened without use of a can opener or other tool. For some years, the most popular can ends of this type were those in which a ring was provided for finger insertion, which when pulled removed a section of the can end along score lines. The ring tab and the removed section of the end were then discarded. This was undersirable for a variety of reasons perhaps chiefly those of unsightly litter; and so a new type of can end was developed which could be opened without the use of tools, but which did not result in any of the components of the can end becoming detached from the can.
Typically in the prior art, such can ends and tabs were both made of aluminum. However, with the well known recent rise in cost of electrical power, aluminum has become a disfavored material for applications where steel can be used, inasmuch as aluminum is, in general, made by electric refining processes which consume enormous quantities of electricity. Therefore, wherever possible, it is desired to substitute steel for aluminum.
In the can end making art, however, steel has been a disfavored material for a number of reasons, chief among those being corrosion. Although steel is preferred for reasons of economy and for certain reasons of ease of manufacture which will be discussed in more detail below, steel has not been a preferred material for tab ends. The present invention involves a steel for tabs coated with a metal chosen to reduce corrosion by means of sacrificial oxidation. It has been found by the applicant that if a steel tab is coated with a material having a higher electronegative potential, that material will be attacked in preference to the steel and if the material is so chosen that a certain amount of oxidation only is permitted, then the tab end will rapidly form its own protective corroded layer which will prevent any further corrosive attacks upon a tab end.